1. Field of the Invention
The present invention relates to a method of welding a hollow member and an insertion member to form a composite member comprised of a hollow member such as a valve structure of a fuel injection system and an insertion member which is inserted into and joined to the hollow member and, more particularly, relates to a method of welding a hollow member and an insertion member to form a composite member comprised of a hollow member and insertion member where a high dimensional accuracy is required in the axial end-to-end distance of the end faces and where a reliable concentricity is required in the center axes of the hollow member and insertion member.
2. Description of the Related Art
An example of the valve structure of a fuel injection system in an internal combustion engine of the related art where concentricity is required will be explained first. As shown in FIG. 14(a) and FIG. 14(b), the valve structure 3 of the related art is comprised of a cylindrical hollow member 11 having a closed bottom, that is, a holder, a cylindrical body 315 to be inserted into and accommodated in the hollow member 11, and an insertion member 12 to be inserted in the hollow member 11.
The overlap portion 13 where the hollow member 11 and the insertion member 12 overlap and the overlap portion 331 where the hollow member 11 and the body 315 overlap are circumferentially welded together.
Next, another example of the valve structure of a fuel injection system in an internal combustion engine of the related art where a high dimensional accuracy is required in the end-to-end distance of the end faces will be explained.
As shown in FIG. 13(a) and FIG. 13(b), the valve structure is comprised of a cylindrical housing 1091, a nozzle receiver 9200 comprised to be able to receive the nozzle portion 1500, a body 1092 provided with an injection bore 9290 communicating with the nozzle holder 9200, a needle 1015 provided with the nozzle portion 1500, and a holding member 1016 provided with a spring 1600 for holding the needle 1015.
In the related art, the body 1092 is inserted into one end of the housing 1091 and the needle 1015 held in the holding member 1016 is inserted into the other end to thereby assemble the parts and form the valve structure 1009.
The overlap portion 1093 of the housing 1091 and the body 1092 is circumferentially welded together. Reference numeral 094 indicates the weld.
Thermal strain occurs at the time of circumferentially welding the overlap portion 1093 and sometimes results in deviation of the dimensions of the valve structure in the axial direction from the desired values.
In the valve structure 1009, the clearance C shown in FIG. 13(b) has to be of a predetermined dimension.
Therefore, in the related art, a spacer 1097 was arranged behind the body 1092 as shown in FIG. 13(b) to absorb the thermal strain at the time of circumferential welding and thereby ensure a suitable clearance C and a suitable range of operation of the needle 1015.
In the related art, the dimensions of A and B shown in FIG. 13(b) are measured at the time of assembling the parts, and the body 1092 etc. are ground to obtain the suitable clearance C. Next, the housing 1091 and the body 1092 are circumferentially welded to join them. The thermal strain accompanying the circumferential welding is absorbed by the spacer 1097.
Therefore, it is possible to obtain a valve structure 1009 resistant to the effects of changes in dimensions due to thermal strain and having precise dimensional accuracy.
Summarizing the problem to be solved by the invention, since thermal strain occurs at the time of circumferential welding in a valve structure of a fuel injection system of the related art where concentricity is required, even if the hollow member 11 and the insertion member 12 are assembled to have the same center axes G1 and G2, there is the problem that the center axes G1 and G2 become misaligned as shown in the later explained FIG. 18(a), FIG. 18(b), and FIG. 19 in the later circumferential welding. Note that from here on, the state where the center axes G1 and G2 are correctly aligned will be referred to as xe2x80x9cgood concentricityxe2x80x9d, while the state where they are not aligned will be referred to as xe2x80x9cpoor concentricityxe2x80x9d.
Further, in the valve structure of the other related art where a high dimensional accuracy is required in the axial end-to-end distance, the spacer 1097 has to be separately provided. Not only is the trouble of assembly increased, but also, while it is possible to absorb the thermal strain by the spacer 1097 in the structure of FIG. 13(a) and FIG. 13(b) shown in the related art, this technique does not work well with other structures. Further, there is a limit to how far the dimensional changes caused by thermal strain can be minimized.
An object of the present invention is to provide a method of welding a hollow member and an insertion member to form a composite member giving a superior concentricity and a high dimensional accuracy in the axial direction.
According to a first aspect of the present invention, there is provided a method of welding a hollow member and an insertion member to form a composite member comprising preparing a hollow member and an insertion member, inserting the insertion member in the hollow member, and partially welding an overlap portion where the hollow member and the insertion member overlap to correct an axial end-to-end distance of the hollow member and the insertion member in a corrective welding step.
Preferably, the method further comprises that the hollow member and the insertion member are joined together by a partial weld provided in the corrective welding step.
Alternatively, the method further comprises circumferentially welding the entire circumference of the overlap portion of the hollow member and the insertion member in a regular welding step.
More preferably, the method further comprises simultaneously performing the corrective welding step and the regular welding step by a plurality of welding heads.
Still more preferably, the method further comprises that said insertion member is press-fitted in the hollow member.
Still more preferably, the method further comprises that at least one set of partial welds are provided at axially symmetric positions (A-H) at the overlap portion in the corrective welding step.
Still more preferably, the method further comprises measuring the axial end-to-end distance of the composite member for each corrective welding step in a measurement step and continuing the corrective welding step until the axial end-to-end distance reaches a predetermined length.
Alternatively, still more preferably, the method further comprises determining an amount of melting before the corrective welding step in a melting determination step and performing the corrective welding step in accordance with the amount of melting determined in the melting determination step.
According to a second aspect of the present invention, there is provided a method of welding a hollow member and an insertion member to form a composite member comprising preparing a hollow member and an insertion member, inserting the insertion member in the hollow member, and partially welding an overlap portion of the hollow member and the insertion member correct the concentricity of the composite member in a corrective welding step.
Preferably, the method further comprises that the hollow member and the insertion member are joined together by a partial weld provided in the corrective welding step.
Alternatively, the method further comprises circumferentially welding the entire circumference of the overlap portion of the hollow member and the insertion member in a regular welding step.
Alternatively, the method further comprises consecutively performing the corrective welding step and the regular welding step.
More preferably, the method further comprises measuring an amount of deviation and direction of deviation of concentricity of the composite member for each corrective welding step and continuing the corrective welding step until the amount of deviation and direction of deviation of concentricity fall within a desired range.
Still more preferably, the method further comprises determining the partial weld formation position and an amount of melting in accordance with basic data collected in advance about the amount of deviation and direction of deviation of concentricity and performing the corrective welding step in accordance with the amount of melting determined in the melting determination step.
According to a third aspect of the present invention, there is provided a method of welding a hollow member and an insertion member to form a composite member comprising preparing a hollow member and an insertion member, inserting the insertion member in the hollow member, measuring a direction of deviation of concentricity of the composite member in a measurement step, and welding the entire circumference of an overlap portion where the hollow member and the insertion member overlap using as a weld start a position opposite in direction to the direction of deviation of concentricity.
Preferably, the method further comprises measuring an amount of deviation of concentricity in the measurement step and setting a position of a welding end so that a length of welding overlap after the circumferential welding changes in accordance with the amount of deviation.
According to a fourth aspect of the present invention, there is provided a method of welding a hollow member and an insertion member to form a composite member comprising preparing a hollow member and an insertion member, inserting the insertion member in the hollow member, measuring a direction of deviation and an amount of deviation of concentricity of the two in a measurement step, and circumferentially welding the entire circumference of an overlap portion where the hollow member and the insertion member overlap by making a plurality of welding heads arranged axially symmetrically rotate relative to the circumference of the overlap portion when the amount of deviation of concentricity measured in the measurement step is within an allowable range.
Preferably, the method further comprises partially welding the overlap portion to provide a partial weld at a position opposite in direction to the direction of deviation after circumferentially welding the overlap portion so as to correct the concentricity of the composite member in a corrective welding step when the amount of deviation of the concentricity measured in the measurement step is outside the allowable range.
Alternatively, the method further comprises changing an amount of melting when providing the above partial weld in accordance with the amount of deviation of the concentricity measured in the measurement step.
More preferably, the method further comprises welding the entire circumference of the overoverlap portion using a single welding head using as a weld start a position opposite in direction to the direction of deviation of concentricity when the amount of deviation measured at the measurement step is outside an allowable range.
Still more preferably, the method further comprises measuring an amount of deviation of the concentricity in the measurement step and setting a position of a welding end so that a length of welding overlap after said circumferential welding changes in accordance with that amount of deviation.
Still more preferably, the method comprises that said insertion member is press-fitted in the hollow portion.